Indirectly heated cathode



Aug. 16, 1938. M. KNOLL E1" AL INDIRECTLY HEATED CATHODE Filed July 10,1934 ATTORNEY Patented Aug. 16, 1938 UNITED stares PATENT OFF2,126,894.: 1 lNB-IRECTLY CATHOD E... Max Knoll and Rudolf R-z'ehnllra,Berlin,- Germany, assignors te Telefunken 'Gcsellschaft:

fiir Drahtlcse Telegraphic m. b. 11., Berlin, Germany, a corporaticn ofGermany Application July 4 Claims.

anode; hence, this that the electron pencil emitted by the cathode mustbe capable of being acted upon by the so called Wehnelt or focusingcylinder of a similar control means.

For these reasons, the form of indirectly heated cathode for Braun tubesheretofore generally em- In order to obviate the drawbacks associatedtherewith, i. e.,

sion substance, according to this invention.

In Braun tubes for television work, when using a form for the indirectlyheated cathode according to this invention, there results still anotherlower than under otherwise equal conditions.

A number of embodiments according to this in- 10, 1934, Serial No. InGermany May 4, 1933' vention shall be described in what follows byreference to the accompanying drawing.

Referring to Fig. 1, l9 denotes the heater wire of the indirectlyincandesced cathode, H is a sheet of metal positioned at right angles tothe tube axis which is indicated by the line A, B. The

the filament H] by hard-soldering (brazing) or may be welded togethertherewith at the point marked P, if desired, by the aid of a sheet-metalstrip 0.

Referring to Fig. 2, the reference symbols I ll,

A, B, K, have the right angles to the tube axis A, B, and it supportsthe electron emlssive substance K upon its face turned towards theanode. The sheet [2 at the end opposite or turned away from the anodehas an extension or projection I 3 which is either welded together withthe heater H1 or is merely secured thereon by clamping action.

According to another embodiment of this invention as illustrated InFigs. la-4c are shown embodiments of the invention in which theelectron-emissive sub- The body being indirectly incandesced by theheater Winding and denoted by I I, in Fig. 1, by l2 in Fig. 2, and M inFigs. 3 and 4, consists Having thus described the invention what weclaim and desire to secure by Letters Patent is:

1. An unshielded point-source thermionic cathode comprising a hollowmetallic cylinder closed at one end by a hollow solid of revolutionhaving a projection of maturely reduced diameter at its apex, anon-conducting hollow cylinder planarly closed at one end disposedwithin the first of said cylinders with said planar surface adjacent tothe closed end of the first of said cylinders, a filament windingdisposed longitudinally within the second of said cylinders, and athermionic emissive coating on the end portion of the exterior surfaceof the projection of the first of said cylinders.

2. An unshielded point-source thermionic cathode comprising a hollowmetallic cylinder closed at one end by a hollow flllStllLlIl of a cone,having a tip on its axis, a non-conducting hollow cylinder planarlyclosed at one end, disposed within the first of said cylinders with saidplanar surface adjacent to the closed end of the first of saidcylinders, a filament winding disposed longitudinally within the secondof said cylinders, and a thermionic emissive coating on the end portionof the exterior surface of the tip of the first of said cylinders.

3. An unshielded point-source thermionic cathode comprising a hollowferro-magnetic cylinder closed at one end by a hollow frustum of a conehaving a tip on its axis, a non-conducting hollow cylinder planarlyclosed at one end, disposed within the first of said cylinders with saidplanar surface adjacent to the closed end of the first of saidcylinders, a filament winding disposed longitudinally within the secondof said cylinders, and a thermionic emissive coating on the end portionof the exterior surface of the tip of the first of said cylinders.

4. An unshielded point-source thermionic cathode comprising a hollowferro-magnetic cylinder closed at one end by a hollow solid ofrevolution having a projection of reduced cross sectional area at itsapex, a non-conducting hollow cylinder planarly closed at one end,disposed within the first of said cylinders with said planar surfaceadjacent to the closed end of the first of said cylinders, a filamentwinding disposed longitudinally within the second of said cylinders, anda thermionic emissive coating on the end portion of the exterior surfaceof the projection of the first of said cylinders.

MAX KNOLL. RUDOLF RZEI-IULKA.

